The present invention relates to vehicle powertrains, more particularly to a dry-plate clutch for a vehicle transmission having an improved combination of stiffness, strength and thermal capacity without increasing the installation space requirements for said dry plate clutch.
Dry plate clutches are used in manual and automated vehicle transmissions to facilitate start-off from rest and disengage the transmission from the engine at shifts. Particularly when starting off, beat will be generated in the sliding surfaces in contact as torque is being transferred during the transition from disengaged to fully engaged state. This heat is absorbed as a temperature increase of the parts in contact. The heat is then, in a rather slow way, conducted and radiated to the surrounding. Due to this slow heat dissipation, quite a large mass is required for absorbing the heat generated while keeping the temperature increase limited. Thus, dry plate clutches are relatively heavy. That requires a stiff and strong suspension in order to carry a dry plate clutch. Moreover, dry plate clutches are bulky, which may lead to conflicts with available installation space, especially in axial direction.
Dry plate clutches comprise a primary side, also referred to as the driving or input side, rotationally connected to an engine, and a secondary side also referred to as the driven or output side, that is rotationally connected to a transmission input shaft. In order to facilitate gear shifting, the secondary side, also referred to as the driven disc, has low inertia.
Therefore, the thermal mass is allocated to the primary side of the clutch. The primary side has an axially moveable clutch plate, referred to as the pressure plate that selectably can clamp and release the driven disc for engaging and disengaging the clutch.
In general, the primary side is fixed to a prime mover, such as an engine flywheel. There are two basic types of construction of the primary side with respect to how the flywheel is used.
Most common is the construction where the engine flywheel has a friction surface facing the driven disc, and hence is a functional pan of the clutch. The pressure plate is located on the other side of the driven disc. An example of such an arrangement is shown in DE10304502A1. The mass of the flywheel is not only used for levelling out engine torque i0 fluctuations, but can also absorb heat generated in the clutch.
Less common, but still frequent, is the primary side construction where the engine flywheel has no other use for the clutch than to suspend it to, and transfer torque from, the engine crankshaft. Instead, the pressure plate faces the flywheel and crankshaft end. This will be referred to as “inverted construction” in the subsequent text. An example of a clutch with an inverted construction can be found in DE10220205A1. Inverted construction clutches are often used when the connection to the engine crankshaft is a sheet metal part. It is also common in dry plate clutches for dual clutch transmissions, e.g. as shown in DE10018646A1.
Normally, more axial space is needed when there is no clutch friction surface on the flywheel. That can lead to compromises between conflicting requirements. On one hand, there must be sufficient thermal mass for the pressure plate. On the other hand, sufficient strength and stiffness is required for the flywheel or the corresponding part that carries the clutch.
Consequently, there is a need for an axially compact dry plate clutch of inverted construction that enables high thermal mass of the pressure plate as well as high strength and stiffness of the device that connects the primary side of the clutch to the engine crankshaft. It is desirable to provide an improved dry plate clutch of inverted construction that solves the above problems.
According to a preferred embodiment, an aspect of the invention relates to a dry-plate clutch of inverted construction in a vehicle transmission. The dry-plate clutch will be referred to as “the clutch” in the subsequent text. The clutch comprises a clutch structure with a connecting device drivingly connected to a prime mover. A pressure plate is rotationally fixed and axially displaceable relative to the clutch structure. A driven disc is connected to a driven shaft and is located between the clutch structure and the pressure plate. The clutch further comprises an actuator means arranged to displace the pressure plate between an engaged state, where the driven disc is clamped between the clutch structure and the pressure plate, and a disengaged state, where the disc is rotatable relative to the clutch structure. The actuator means can comprise any suitable device for actuating the clutch, such as a hydraulic or pneumatic cylinder or an electric motor.
The connecting device is provided with hollow sections, or recesses, at a number of angular locations extending into a radial surface facing the pressure plate. The pressure plate has corresponding axially extending protrusions in a radial surface facing the connecting device, which protrusions at least partially extend axially into the hollow sections in the disengaged state. The corresponding hollow sections and protrusions are located so that the rotational balance of the component parts is retained. For individual hollow sections and protrusions this requires two or more such features in the respective component.
According, to one example, the hollow sections can extend axially at least partially through the connecting device. Alternatively, the hollow sections can extend axially fully through the connecting device.
The protrusions have a circular or oval cross-section and can be equally distributed around the radial surface of the pressure plate. Alternatively, the protrusions have a rectangular, triangular or trapezoidal cross-section. The protrusions can be arranged as two identical protrusions at opposite sides of the rotational axis and at the same radius from this axis. Alternatively, multiple protrusions can be equally distributed around the face of the pressure plate. The protrusions can have the same or different sizes and be arranged on the same or at different radii.
The protrusions can also have a honeycomb cross-section, wherein they can be provided as a pattern over an annular section of the pressure plate where it faces the connecting device.
According to a further example, the protrusions can comprise two or more ring segments. Such ring segments can have an intermittent annular cross-section, wherein the interrupted sections allow for radial reinforced portions between adjacent recesses in the connecting device. The protrusions can be arranged as a single ring or as concentric rings.
The connecting device with its hollow sections can comprise a cast component. Manufacturing the connecting device as a cast part with the hollow sections formed in the casting process, enables cost-effective production. Alternatively it can comprise a metal sheet component with cut-out sections, e.g. by blanking. Manufacturing the connecting device as a sheet metal part were the hollow sections are cut out also enables cost-effective production.
Alternatively, the invention relates to a dual dry plate clutch in a vehicle transmission. The dual clutch transmission comprises a clutch structure with a connecting device arranged to be drivingly connected to a prime mover. The prime mover can be an internal combustion engine or an electric motor. A first and a second pressure plate are rotationally fixed and axially displaceable relative to the clutch structure. A first and a second driven disc are connected to a first and a second driven shaft, respectively, and are located between the clutch structure and their respective pressure plate. A first and a second actuator means is arranged to displace their respective pressure plates alternately between a disengaged state and an engaged state, wherein one driven disc is clamped between the clutch structure and one pressure plate white the other driven disc is rotatable relative to the clutch structure and other pressure plate. The operation of dual clutch transmissions is well known in the art and will not be described in further detail. The dual clutch transmission comprises one dry-plate clutch according to the invention adjacent the connecting device, which clutch has been described above.
The invention further relates to a vehicle provided with a transmission comprising a dry-plate clutch as described above.